[SOLVED] 604 &gt; 605 upgrade bizarre issue

I've upgraded Zimbra 6.0.4 OSE (os centos 5.4) to 6.0.5, whole procedure seemed to be perfect. However, next day some emails started getting screwed up by zimbra. That is, there is destination email in the "From" field instead of original sender's, as if user sent it to himself. 2 users reported this problem so far. I can't figure out any regularity as to when that happens, but automatic notifications seem to affected more frequently. How do I debug it?

Edit: nevermind, it turned out to be a strange combination of domains and filters they had.